If you want to start it slow, it takes about 4 to 6 weeks for freshwater tank. Longer for salt water. to speed up the process, you can buy marc weisz bacter boost. Add a capful per 50 gal into your tank. crush a bit of flake food and put it in. 2 days later, add another capful. you can then slowly add a few fish at a time into your tank. You should start with hardy fish first then move up to other fish.